The present invention generally relates to a method and device for butt-welding metal strips together by employing a laser beam for cutting and welding.
In the past, there have been various attempts to provide an acceptable method for butt-welding metal strips. One such attempt, known as flash butt-welding, involves joining contiguous ends of a leading (take-up) coil or sheet metal roll and a trailing coil by resistance welding Another butt-welding technique has been to weld the ends of the leading coil and the trailing coil using pipe welding electrodes. The plasma welding method is also known, as is the use of clinches whereby the coil ends are joined together by stamping.
All of these methods incur the development of weld reinforcement. This can result in a leading coil that is not round when wound up. In addition, the roller pass can be damaged. Further, with thin strip material, the weld reinforcement presses into the coil. The plasma welding method suffers from an additional disadvantage due to the higher heat transfer in the weld pursuant to the wider heat influence zones, which results in the hardening of the weld zones with poor forming qualities. This disadvantage is shared by the microplasma welding method, which is used for welding very thin strips together.
A further method and device for butt-welding steel strip disclosed in European Patent EP-OS 0 151 848. In this technique, the strips are cut mechanically and then welded together by a laser beam. The expense incurred with this device is relatively high.
It is therefore desirable to provide an efficient method and device for butt-welding metal strips which avoids the development of weld reinforcement and associated disadvantages and which results in a strong weld. It is further desirable to provide a device which requires only a single laser and which allows for continuous operation of the leading coil.